1. Field of the Invention
The present invention relates to improved wire bonds with the bond pads of semiconductor devices and the lead frames associated therewith. More specifically, the present invention relates to improved wire bonds with ball bumps previously made on the bond pads of semiconductor devices.
2. State of the Art
In semiconductor device manufacture, a single semiconductor die (or chip) is typically mounted within a sealed package. In general, the package protects the semiconductor die from damage and from contaminants in the surrounding environment. In addition, the package provides a substantial lead system for connecting the electrical devices formed on the die to a printed circuit board or other external circuitry.
Each semiconductor die has a lower surface (commonly referred to as the back of the die) that is devoid of circuitry, and an upper surface (commonly referred to as the active surface or face of the die) having integrated circuitry constructed thereon. The integrated circuitry is electrically accessible via bond pads located on the active surface of the semiconductor die which may be arranged in a wide variety of patterns, such as around the periphery of the semiconductor die, the center of the semiconductor die, or both, etc.
Typically the initial component in the packaging process is a lead frame. The lead frame is a metal frame which supports the semiconductor die for packaging and provides the leads for the final semiconductor package. A typical lead frame strip is produced from metal sheet stock (usually a copper, copper alloy, alloy 42, etc.) and is adapted to mount the semiconductor die.
A conventional lead frame has the semiconductor die adhesively mounted on a die paddle of the lead frame while the lead fingers (leads) extend around the periphery of the semiconductor die (the edges) terminating adjacent thereto. Subsequently, wire bonds are made to connect the bond pads on the active surface of the semiconductor die to the appropriated lead finger of the lead frame. After the wire bonding operation, the lead frame and semiconductor die are encapsulated in a transfer die molding process. After encapsulation, the lead frame is trimmed with the remainder of the individual lead fingers being formed into the desired packaging configuration.
One of the problems associated with conventional lead frame configurations is that, with the decreasing size of the semiconductor die and the increasing amount of circuitry included in the semiconductor die, it is necessary to connect an ever- increasing number of bond pads on the active surface of the semiconductor die with an ever increasing number of lead fingers of the lead frame. This requires that the bond pads on the semiconductor die be located on smaller pitch spacings and the width of the lead fingers be smaller. This, in turn, leads to smaller wire bonds on both the bond pads of the semiconductor die and the lead fingers of the lead frame which causes the wire bonds to be more highly stressed by the forces placed on them.
In a Lead-Over-Chip (LOC) type lead frame configuration for an integrated circuit semiconductor device, the lead fingers of the lead frame extend over the active surface of the semiconductor die being insulated therefrom by tape which is adhesively bonded to the active surface of the semiconductor die and the bottom of the lead fingers. In this manner, the semiconductor die is supported directly from the lead fingers of the lead frame. Electrical connections are made between the lead finger of the lead frame and the bond pads on the active surface of the semiconductor die by way of wire bonds extending therebetween. After wire bonding, the lead frame and semiconductor die are encapsulated in suitable plastic material. Subsequently, the lead fingers are trimmed and formed to the desired configuration to complete the packaged semiconductor device assembly.
One of the shortcomings of the prior art LOC semiconductor die assemblies is that the tape used to bond to the lead fingers of the lead frame does not adequately lock the lead fingers in position for the wire bonding process. At times, the adhesive on the tape is not strong enough to fix or lock the lead fingers in position for wire bonding as the lead fingers pull away from the tape before wire bonding. Alternately, the lead fingers will pull away from the tape after wire bonding of the semiconductor die but before encapsulation of the semiconductor die and lead frame, either causing shorts between adjacent wire bonds or the wire bonds to pull loose from either the bond pads of the semiconductor die or lead finger of the lead frame. As before with conventional lead frames, with the decreasing size of the semiconductor die and the increasing amount of circuitry included in the semiconductor die, it is necessary to connect an ever-increasing number bond pads on the active surface of the semiconductor die with an ever-increasing number of lead lingers of the lead frame. This requires that the bond pads on the semiconductor die be located on smaller pitch spacings and the width of the lead fingers be smaller. This, in turn, leads to smaller wire bonds on both the bond pads and the lead fingers of the lead frame which causes the wire bonds to be more highly stressed by the forces placed on them.
Therefore, a need exists for increased strength wire bonds between the lead fingers of a lead frame and the bond pads of a semiconductor die, particularly as the size of the semiconductor die, the size of the bond pads thereon, the size of the lead fingers connected by wire bonds to bond pads, and the pitch thereof all decrease.
It is known in the art to form bumps on the bond pads of semiconductor dice using wire bonding apparatus for subsequent Tape Automated Bonding (TAB) or flip-chip (face-down) assembly of bare chip dice to a substrate. Such is illustrated in U.S. Pat. Nos.4,750,666 and 5,058,798. It is also known to repair defective or broken wire bonds to bond pads of semiconductor dice by forming a flattened pad over the remaining portion of the wire and, subsequently, bonding the end of another wire thereover. Such is illustrated in U.S. Pat. No. 5,550,083. Other types of wire bonding operations on the bond pads of a semiconductor die are illustrated in U.S. Pat. Nos. 5,235,212, 5,298,793, 5,343,064, 5,371,654 and 5,492,863.